The problem with that notion as some have mentioned is that if they had the same actress that played Peggy, playing Sharon, it would just signify even more that Steve isn't ready and hasn't moved on from his past if he's become attached to a woman that resembles Peggy in literally every way; plus it'd be creepy for him to go for a younger woman that looked exactly like her, not to mention that there would be a lot of criticism saying that the only real reason why he went for Sharon is because of her resemblance to Peggy.

At the moment, if they had to cast someone as Peggy, I wouldn't mind someone like Yvonne Strahovski

__________________Kristen Schaal is the greatest and most attractive woman in the 28 known galaxies